Band pass filters are used in a radio's frond end to let pass only wanted frequencies and block or otherwise attenuate frequencies above and below the pass band. A band pass filter in a base transceiver station (BTS) radio is generally made from cavity resonators that are coupled together. It is known for such a cavity resonator to exploit multiple modes (multiple resonant frequencies) in order to reduce the size of the filter. From a design perspective the highest Q per volume is desirable in order to achieve the most compact filter with the lowest insertion loss. The quality or Q factor is a figure of merit for reactive components such as capacitors and inductors that measures energy efficiency; specifically it is a ratio of stored energy to dissipated power per unit time. A resonant cavity is in effect a reactive component in which some external coupling/power source excites electromagnetic fields within the cavity, and it is known to use the Q factor as a design and performance metric for cavity resonators. Also desirable in a practical bandpass filter is flexibility in its operational parameters so the filter can perform a wide variety of filtering functions to optimally meet the specifications needed for a given deployment. What is needed in the art is a compact band pass filter with a very low insertion loss that also has great design flexibility.
In this regard two prior art filters are relevant:                The Black Hole Filter by the KMW company of Hwasung, Korea; see http://www.kmw.co.kr/eng/product/product_new_3.html, last visited Nov. 17, 2016) is made from a ceramic sphere loaded cavity operating with triple transverse-electric (TE) modes.        The Seven-pole UMTS filter by Radio Frequency Systems of Meriden, Conn., USA (see http://www.rfsworid.com/stayconnected/index.php?p=657&1=1&listName=stayconnected_en_articles&indexVal=67 last visited Nov. 17, 2016) is a ceramic filter with triple transverse-magnetic modes in a cubic format.        